Acoustic substrate

ABSTRACT

A micromachined microphone or speaker embedded within, or positioned on top of, a substrate suitable for carrying microelectronic chips and components. The acoustic element converts sound energy into electrical energy which is then amplified by electronic components positioned on the surface of the substrate. Alternatively, the acoustic element may be driven by electronics to produce sound. The substrate can be used in standard microelectronic packaging applications.

FIELD OF THE INVENTION

The present invention relates to micromachined microphones and speakersand, more particularly, to an acoustic device that is microfabricateddirectly within or on a laminate substrate or lead frame. This enablesnew manufacturing processes to be applied to the manufacture ofmicroacoustic devices, and making it easy to integrate into standardprinted circuits and microelectronic packages.

BACKGROUND OF THE INVENTION

Micromachined microphones, often called “MEMS microphones” (MEMS refersto micro-electrical mechanical systems), have become an attractivealternative to conventional condenser or electret microphones. Condenserand electret microphones utilize a diaphragm that responds to sound byvibrating. The vibrations of the membrane are monitored by monitoringthe capacitance of the gap between the diaphragm and a conducting platethat is close to the diaphragm. In the case of a condenser microphone,the diaphragm is made from a conductive material and is then chargedusing an external bias (typically in the range of 40V). For an electretmicrophone, the diaphragm is made from a dielectric material, usuallypolymer such as Teflon™, and is permanently charged during manufactureby ion implantation. The movement of the diaphragm in both condenser anddiaphragm is monitored by amplifying the fluctuating voltage on theconductor that sits below the diaphragm. Since the gap between thediaphragm and conductive plate determines the capacitance of the system,the position of the diaphragm determines the electrical signal. Othermethods for monitoring the movement of a diaphragm or ribbon have beendeveloped using magnetic fields. These are known as dynamic microphonessince the velocity of the moving element determines the electricalsignal. Finally, still other methods for monitoring the position of adiaphragm have been developed, for example the use of a laser to monitordeflection or by frequency modulation in an AC circuit. However, themost popular microphone technology, by far, is the electret microphone.

MEMS microphones are now challenging electret microphones for marketacceptance. MEMS microphones are almost exclusively built from siliconsubstrates using semiconductor microfabrication techniques. Since theyuse lithographic semiconductor processes, these microphones can be builtwith precise features and extremely small gaps between the diaphragm andconducting plate below the diaphragm, on the order of a few micrometers.This can increase the sensitivity of the microphone, at least inprinciple. In practice, MEMS microphones are not more sensitive thantraditional microphones because they must use semiconductor-stylematerials such as silicon, silicon dioxide, or silicon nitride which aremuch stiffer than polymer, and because their diaphragm areas aresmaller. However, MEMS microphones can be made smaller than traditionalmicrophones and, since they are made from non-polymer materials, theMEMS microphones can handle higher temperatures than electrets. Thismakes them attractive for integrating in wave soldering manufacturing,where entire printed circuit boards must be exposed to heat in order tosolder all components on the boards at once. Traditional electretmicrophones cannot survive wave soldering, and typically losesensitivity in the process, so must be assembled onto an electroniccircuit after the wave soldering step.

Some MEMS microphones build amplification and digitization electronicsdirectly on the same substrate as the diaphragm. This reduces the sizeneeded for the microphone and, in principle, reduces cost since a secondamplifier chip is not necessary. In practice, cost is not necessarilyreduced because the diaphragm manufacture does not use completelystandard semiconductor processing and so the devices do not benefit fromthe semiconductor process to the same degree as standard CMOS electronicdevices do. Furthermore, the diaphragm itself takes up considerablespace on the silicon which increases cost since the cost of siliconmicrofabrication is almost proportional to surface area of silicon. MostMEMS microphones use separate amplifier chips which are connected to thediaphragm device during final package assembly.

All silicon MEMS microphones suffer from the need to assemble the MEMSdevice together with other electrical components, such as amplifierchips, passive devices and conductive leads, and further to place into aprotective package. The problem with MEMS packaging is well known, andstill plagues the MEMS industry. The MEMS device is typically built on asilicon wafer, but must be cut out and transferred to a metal orlaminate substrate where it is electrically connected to connections onthe substrate. Since the MEMS device is very fragile, this assembly is adifficult and expensive operation and is currently the cost limitingstep in MEMS manufacturing. Any innovations that can simplify oreliminate this step would significantly impact the ability to deployMEMS microphones.

The current state of art does not provide a satisfactory way toconstruct a micromachined microphone or micro-speaker that is trulycompatible with the packaging of the acoustic device and its associatedelectronics. A device that can be readily constructed that is compatiblewith standard packaging techniques would be desirable.

SUMMARY OF THE INVENTION

The various embodiments and examples provided herein are generallydirected to systems and methods for producing micromachined microphonesor speakers on lead frames or laminate substrates. Preferred embodimentscomprise a laminated substrate or metal lead frame where the acousticelements have been fabricated directly within or on the surface of thesubstrate or lead frame. This substrate or lead frame is then used as asubstrate for further packaging operations, such as die attach orcomponent assembly. Effectively, this invention puts the micromachinedmicrophone or speaker in the electronic package material, beforemicroelectronic packaging has commenced.

Microelectronic packaging uses highly developed, advanced manufacturingtechniques. First, a laminate substrate or lead frame is prepared to actas the main surface for the microelectronic components that are to beassembled together. In the case of a lead frame, the starting surface ismade from conductive metal (such as copper) that is precision cut usinglaser or other machining tools to produce conductive leads. Electroniccomponents such as silicon dies are attached to the leads usingadhesives, then electrical connections are made from the component tothe lead frame using thin wires (wire bonding), flip chip soldering,surface mount soldering, or other standard techniques. When allelectrical connections have been made, the device is encapsulated in aprotective polymer to produce a final “packaged” microelectronic chip.

In the case of a substrate, the starting surface is made from laminatedlayers of metal and polymer (typically fiberglass or resin). These maybe constructed to produce complex 3-D arrangements of interconnectswithin the laminate layers. Electronic components such as silicon diesor other elements are attached to the surface of the laminate structureusing adhesives, then tiny electrical connections are made from thecomponent to the lead frame using thin wires (wire bonding), flip chipsoldering, surface mount soldering, or other standard techniques. Whenall electrical connections have been made, the device is encapsulated ina protective polymer or capped using a housing structure to produce afinal “packaged” microelectronic chip.

The present invention describes the fabrication and/or placement of amicromachined microphone or speaker within or on the laminate structureprior to attachment of electronic components on the surface of thelaminate. By natural extension, this invention also describes amicrophone or speaker fabricated on a lead frame prior to electronicattachment.

Other objects and features of the present invention will become apparentfrom consideration of the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

The details of the invention, both as to its structure and operation,may be gleaned in part by study of the accompanying figures, in whichlike reference numerals refer to like parts. The components in thefigures are not necessarily to scale, emphasis instead being placed uponillustrating the principles of the invention. Moreover, allillustrations are intended to convey concepts, where relative sizes,shapes and other detailed attributes may be illustrated schematicallyrather than literally or precisely.

FIG. 1 is across sectional view of the acoustic substrate showing theacoustic element buried within a laminate structure and amicroelectronic chip mounted on the surface.

FIG. 2 is a perspective view of an acoustic diaphragm element integratedwith laminate materials.

FIG. 3 is a perspective view of acoustically sensitive resonator arrayelement integrated with laminate materials.

FIG. 4 is a perspective view of acoustically sensitive ribbon elementintegrated with laminate materials.

FIG. 5 is a cross section view of an acoustic element buried underlaminate allowing more space for more electronic components.

FIG. 6 is a cross section view of an acoustic element in laminate wherethe laminate is used as part of protective package instead of base forelectronic chip attachment.

FIG. 7 is a cross section view of typical laminate substrate showinglaminate layers and vias.

FIG. 8 is a diagram showing a method for fabricating an acoustic elementwithin a substrate.

FIG. 9 is a diagram showing method of fabricating an acoustic elementwith an electret and with all-air gap.

FIG. 10 is a diagram showing second method for creating free-standingstructure in laminate.

FIG. 11 is a diagram showing third method for creating free-standingstructure in laminate.

FIG. 12 is a diagram showing method fabricating an acoustic element withan electret and with all-air gap.

FIG. 13 is a diagram showing method for fabricating an acoustic elementon a lead frame.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Each of the additional features and teachings disclosed below can beutilized separately or in conjunction with other features and teachingsto provide an acoustic sensor or actuator that is embedded or on thesurface of a laminate substrate or lead frame. Representative examplesof the present invention, which examples utilize many of theseadditional features and teachings both separately and in combination,will now be described in further detail with reference to the attacheddrawings. This detailed description is merely intended to teach a personof skill in the art further details for practicing preferred aspects ofthe present teachings and is not intended to limit the scope of theinvention. Therefore, combinations of features and steps disclosed inthe following detail description may not be necessary to practice theinvention in the broadest sense, and are instead taught merely toparticularly describe representative examples of the present teachings.

Moreover, the various features of the representative examples and thedependent claims may be combined in ways that are not specifically andexplicitly enumerated in order to provide additional useful embodimentsof the present teachings. In addition, it is expressly noted that allfeatures disclosed in the description and/or the claims are intended tobe disclosed separately and independently from each other for thepurpose of original disclosure, as well as for the purpose ofrestricting the claimed subject matter independent of the compositionsof the features in the embodiments and/or the claims. It is alsoexpressly noted that all value ranges or indications of groups ofentities disclose every possible intermediate value or intermediateentity for the purpose of original disclosure, as well as for thepurpose of restricting the claimed subject matter.

The various embodiments provided herein are generally directed tosystems and methods for producing acoustic elements that can be embeddedwithin laminate substrates, or fabricated on the surface of laminatesubstrates or lead frames. A preferred embodiment comprises a laminatesubstrate consisting of a conducting layer, a non-conducting layer, anda second conducting layer built on the non-conducting layer. The secondconducting layer is patterned to produce free-standing structures with acavity that is formed between the free-standing structures and thenon-conducting layer. This can be performed through a variety of means,such as providing an offset for the free-standing structures, or byproducing an opening in the non-conducting layer. When oscillating airpressure is present (in the form of sound), the free-standing structurescan move with the sound waves and their positions electronicallydetected by the first conductive layer. Electrical detection can occurthrough conventional means such as monitoring the changing capacitancewith a resonance circuit, or by biasing one of the two conductive layersand amplifying the resulting signal.

Referring to FIG. 1, the basic device comprises a laminate structure (2)comprising multiple layers (3), preferably conductive and non-conductivelayers. Laminates are usually films or foils that are bonded togetherusing adhesive and pressure to produce a single flat substrate thatconsists of the films and foils as layers in the substrate. Othervarieties of laminates are also common, such as those formedlithographically by photo-sensitive polymers. An acoustically sensitiveelement (4) is placed or formed within a cavity (6) which is formed fromopenings in the layers (3). The element (4) makes electrical contactwith one or more conductive layers in the laminate. The cavity (6) aboveand below the acoustically sensitive element (4) may be covered withmore laminates encasing the acoustically sensitive element within anenclosed cavity. Openings or ports (8) in laminate layers (3) may beformed to provide access for air which will increase sensitivity of theacoustic element (4). Alternatively, the acoustic element (4) may befully exposed to air. The substrate (2) thus formed may be used as abase substrate for further assembly of electrical components such aselectronic chips (10) which are bonded to the substrate and electricallyconnected to conductive elements on the substrate using conventionalmeans, such as wire bonds (12), flip chip bonding, surface mountsoldering, and the like.

Many types of acoustic devices can be used as the acoustic element. Wedescribe three types of devices here: a diaphragm device, amulti-resonator device, and a ribbon device. Referring to FIG. 2, theacoustic element (4) consists of a laminate layer (22) with a thindiaphragm layer (24) that is suspended above a conductive base layer(26). The thin diaphragm (24) may be made from a conductive materialforming a capacitor (condenser microphone), or from an insulatingmaterial that is given an electric charge (electret microphone). Thediaphragm (24) may have openings (28) such as holes (“release holes”) toaid in the passage of etching chemicals during manufacture. In apreferred embodiment, the thin diaphragm (24) is connected to a secondconductive layer (30) in the laminate (22), which is in turn patternedto produce an electrical trace (32) which can be connected to otherconductive traces in the laminate material.

The conductive base layer (26) is made from one of the conductive layersin the laminate, which is patterned to produce an electrical trace whichcan be connected to other conductive traces in the laminate materialsuch as vias (34). The conductive traces in the laminate material arepatterned to produce convenient connection pads for electroniccomponents such as an amplifier.

In the presence of alternating air pressure, the diaphragm (24) movescausing a change in capacitance which can be detected by an amplifierthat connects to one or both of the conductive traces (32) and (34).This description describes a direct air gap between the diaphragm (24)and the base conductor (26). In an alternate embodiment, an additionalnon-conducting layer may be positioned between the air gap and theconducting base to prevent accidental short circuit between theconductive diaphragm (24)and the conductive base layer (26), or to easefabrication. In another alternate embodiment of this acoustic device(4), the diaphragm (24) may be made of an insulating, charged materialand the base layer (26) may be made of a conducting material to form anelectret microphone. In another alternate embodiment of this acousticdevice (4), the diaphragm (24) may be made of conductive material andthe base layer (26) may be made of an insulating, charged material toform an electret microphone.

Referring to FIG. 3, the acoustic element (4) may consist of a laminatelayer (42) supporting resonating elements such as cantilevers (44).These elements (44) resonate in sympathetic vibration with thealternating air pressure. By using multiple resonators, or by designingresonating elements with many resonant modes, a broadband frequencyresponse can be obtained. Since the acoustic elements work in resonantoperation, the device is capable of higher sensitivity than a normaldiaphragm.

The resonating elements (44) are suspended above a conducting layer (46)as with the diaphragm. As with the diaphragm, electrical contacts (48)are made to the resonating layer (44) and patterned into conductivetraces (50) that can be routed through the laminate structure. The baseconductor (46) is also patterned to form traces (52) which can be routedthrough the laminate, including through vias.

This description describes a direct air gap between the resonators (44)and the base conductor (46). In an alternate embodiment, an additionalnon-conducting layer may be positioned between the air gap and theconducting base (46) to prevent accidental short circuit between theconductive resonators (44) and the conductive base layer (46), or toease fabrication. In another alternate embodiment of this acousticdevice(4), the resonating elements (44) may be made of conductivematerial and the base layer (46) may be made of a charged insulatingmaterial, forming an electret microphone.

Referring to FIG. 4, the acoustic element (4) may consist of a laminatelayer (62) supporting a thin ribbon (64) formed of conductive material.The ribbon (64) may be shaped to form a corrugated structure or ameandering structure in order to reduce the effective spring constant ofthe ribbon (64). The ribbon (64) is held in place over a supportinglayer (66) by the laminate layer (62). Changing air pressure moves theribbon material (64). If the ribbon (64) is placed in the presence of amagnetic field, formed using an external magnet (not shown), thenmovement in the ribbon (64) will result in an induced voltage in theribbon. This voltage can be routed to an amplifier by conductive traces(68) patterned on the layer (62) which can be routed, if desired, todifferent layers by vias (70). Additionally, magnetic materials such aspermalloy may be added in the form of laminate layers to improve themagnetic field surrounding the ribbon.

Referring to FIG. 5, the laminate substrate (82) may completelyencapsulate the acoustic element (84) within a cavity (86). Furtherlaminates may be added to enclose the acoustic element (84), providingopenings (88) for air to pass at convenient locations (88). This may bedone to protect the acoustic element (84), or to improve acousticproperties, or to create more surface area for components to beassembled above the acoustic element area. If laminate layers are usedto completely cover the active area, i.e., the acoustic element (84),more room will be made available for electronic components (90) to bemounted to the substrate (82) and electrically connected to conductiveelements using conventional means such as, e.g., wire bonds (92). Thiscan reduce the overall size of the packaged device. Additionally, theacoustic area may be made very large since electrical components (90)may be mounted directly above (or below) the acoustic element (84).

Referring to FIG. 6, the acoustic substrate (110) may be used as part ofa microelectronic package housing instead of a base plate on which toattach microelectronic parts. In this embodiment, a standard laminatesubstrate (102) is used to mount microelectronic chips (106) which areelectrically connected with connectors (108) to conductors on thesurface. Spacers (104) around the edges of the laminate substrate (102)are used to provide a vertical offset. The spacers (104) provideelectrical connections from the bottom substrate (102) to the toplaminate (110) that contains the acoustic element (112). The toplaminate (100) caps the package, providing protective covering for themicroelectronics (106) and also providing an acoustic function.

These embodiments illustrate the types of acoustic devices that can beembedded within, or mounted on, a laminated substrate. These embodimentsalso illustrate how the acoustic elements may be placed either on thesubstrate surface or buried within the substrate, and that the substratemay be used to mount microelectronic chips or be used for another partof the device package.

Construction of these embodiments and the like may proceed by variousmeans. In the simplest method, the acoustic element may be fabricatedseparately by appropriate means. The acoustic element may then be placedwithin the laminate material prior to laminate bonding, forming anembedded device. Electrical contacts may be made to the acoustic elementprior to lamination through conventional methods such as wire bonding,flip chip bonding, surface mount soldering, solder paste, solderbumping, and the like. To aid in manufacturing yield, the acousticelements may be encapsulated in a temporary protective material, such asa low molecular weight polymer during the lamination process. Thisprotective encapsulant material can be removed later by a suitablemethod such as dissolving in a solvent, etching in an etching solution,etching in a plasma or vapor, or heating to melt or sublimate.

An alternate method would be to build the acoustic element directlywithin the laminate material as part of the manufacturing process forthe laminate substrate. This embodiment is discussed here.

The following first describes the general manufacturing process forproducing laminate substrates, and then describes the modificationsneeded to produce an acoustic element in the substrate. Referring toFIG. 7, laminate substrates (120) are created by first preparing sheets(122) of material, typically polymer resin called “prepreg”, with metallayers (124) bonded to the top, typically copper. The copper layer (124)is patterned using lithography and etch techniques (photoengraving).Holes and other openings (126) (128) (130) are drilled or cut out of thepolymer sheets (122) later using drills, routers, or laser machiningtools. Each layer (122) may be subsequently treated to improve adhesionduring the lamination process. Layers (122) are aligned using alignmentpins or jigs and bonded together, to form a composite laminatestructure. Layers (122) may be bonded one at a time, particularly when“blind vias” or “buried vias” are needed. A via (126) is an electricalcontact that passes through the laminated structure (120). A “blind” via(128) is an electrical contact that passes through several laminatelayers (122) but does not pass all the way through and can be seen onlyfrom one side of the laminate structure (120). A “buried” via (130) isan electrical contact that passes through several layers but cannot beseen from either side of the finished substrate (120). In the case ofblind or buried vias (128) and (130), after each layer is subsequentlybonded to the stack, conductive material is used to fill the holes thatwere drilled prior to bonding. Alternatively, all layers may be bondedin a single step, if buried vias are not needed. Finally, remaining viaholes (126) are filled with metal and the laminate may be coated withpatterned protective layers such as a polymer solder mask.

The following describes different methods for building the acousticelement within the laminate. In the first embodiment, shown in FIG. 8,two halves of the laminate are prepared in advance. The top halfcontains a laminate layer (142) and a first metal foil (144), such ascopper, bonded to the laminate layer (142). A second metal foil (146),such as gold, is patterned over the first metal foil (144). The secondmetal is chosen for good mechanical and electrical properties, andbecause it is resistant to chemicals that would ordinarily etch thefirst metal. The second laminate layer (145) consists of laminatematerial that has a cavity (148) within it. The cavity (148) can becreated using etching, cutting, ablation, drilling or other methods.Beneath the cavity (148) is a third metal foil (150), such as copper.The two halves (142) and (145) are bonded together to place thepatterned metal over the cavity (148). An opening (152) is cut into thetop layer (142) to expose the first metal foil (144). The opening (152)can be created using etching, cutting, ablation, drilling or othermethods. The opening (152) may be created at any time, such as beforethe first foil (144) is bonded to the top laminate (142). Finally, achemical etchant is introduced into the opening to etch the first metalfoil (144). In the preferred embodiment, the etchant may be ammoniumpersulfate or ferric chloride which efficiently etch copper but which donot etch gold. The etching process removes the first metal layer (144)but does not affect the second patterned metal (146). This “releaseetch” leaves a freestanding movable structure (156) which can be used asthe acoustic element. Electrical acoustic of the movable structure canoccur at the third metal layer (150) that monitors the change incapacitance through the cavity (148) and laminate material (158).

A variation of this embodiment may be realized by substituting thesecond layer with a laminate containing a charged electret, as seen inFIG. 9A. In this device, the freestanding structure (162) is suspendedover a cavity (164) which is created in a laminate layer (166) and whichalso contains a charged electret material (168). A still differentembodiment can be accomplished if the design requires an all-air gapbetween the two conductive layers. In this embodiment, a cavity (170) iscreated that passes through the laminate to the third metal foil (172).If the third metal foil (172) is made from a suitably different metalthan the first metal foil (176), the release etching will not harm thismetal layer. Alternatively, layer (174) comprised of a fourth metal maybe patterned over the third metal foil (172). This metal is selected tobe resistant to the etchant used to remove the first metal foil. Thebottom layer (172) of metal is protected during the release etch. Thisleaves two metals (174) and (178) separated by an air gap at thecompletion of etching.

Another embodiment of the manufacturing process is shown in FIG. 10.Here a metal foil (182), preferably copper, is prepared as usual on thesurface of a laminate layer (188). A second metal (184), preferablygold, is patterned on top of the first metal foil, having different etchproperties from the first. A new laminate layer (185) containing anopening (186) is bonded to the first layers (188) to complete thelaminate structure (180). The first metal (182) is etched using anappropriate chemical to leave a thin open cavity (190) below the secondpatterned metal (184), thus releasing the metal and yielding afree-standing structure. Etchant chemical may access the metal foilthrough openings in the patterned metal. The first layer (188) may be adielectric or may contain charged elements making the device anelectret. If the layer (188) is non-conductive, then acoustic of theacoustic element can occur at conductive layers below the non-conductivelayer.

Another embodiment of the manufacturing process is shown in FIG. 11. Inthis embodiment, a top laminate layer (204) is prepared having anopening (202) in it. A metal foil (206), preferably copper, is preparedwith a second metal (207) patterned on its top side and a third metal(208) patterned on its bottom side. The patterned metal is preferablygold. A second laminate layer (210) is also prepared. The two layers arebonded together with the patterned metal foil to form a single laminateconstruction (212). Etchant is introduced through the opening in thesecond patterned metal. The patterned metal should be resistant to theetchant, whereas the foil should be attacked by the etchant. Possibleetchants are ammonium persulfate or ferric chloride which will etchcopper but will not etch gold. Etching chemical can reach the foilthrough openings in the top patterned metal layer. After etching, onlythe patterned metal remains, leaving a free standing structure which isthe acoustic element (214).

A variation on this embodiment is shown in FIG. 12. In this version, acharged dielectric (216) is placed under the patterned metal. Afteretching the metal foil, the freestanding metal is positioned over an airgap (218) and an electret, forming a microphone.

Similar embodiments can be envisioned on substrates that do not havelaminate structure, but are still used for packaging, for instance metallead frames. A metal lead frame is often used for mountingmicroelectronic chips and providing electrical connections to the chip.The lead frame is first cut from a single sheet of metal into itsdesired shape. Following this, microelectronic chips and otherelectrical components are attached to the surface of the lead frame,then electrical connections are made between the chip and the lead frameusing techniques such as wire bonding, flip chip bonding, surface mountsoldering, and the like. Finally, the circuitry is embedded within amold compound which protects the electronics and forms the shape of thefinal packaged product. No MEMS device can survive this process.

The following describes a method for building a microacoustic elementthat can be packaged on a lead frame. The basic procedure is illustratedin FIG. 13. First, a lead frame (222) is created using standard methods,such as cutting. The lead frame (222) should have small holes oropenings in it to allow access to the acoustic section. Second, a metallaminate structure (224) is prepared consisting of a first metal film,with a second metal patterned on top, and a third metal film bonded tothe top. The first and third metals are constructed of a metal,preferably copper, that is different from the middle metal, preferablygold or aluminum. This metal laminate (224) is bonded to the top of thelead frame (226). Electrical connections (228) between the lead frameand the metal sandwich structure are made by any method, such assoldering or metal welding. Following this, the lead frame is used formounting further microelectronic parts such as chips and passivecomponents. Parts (230) are mounted and electrically connected usingindustry standard methods, such as pick-and-place, wire bonding, flipchip bonding, surface mount soldering, and the like. The assembly isthen encapsulated in protective material (232) such as epoxy usingnormal packaging methods. After encapsulation, etchant is allowed topenetrate through the access holes in the lead frame to etch the metallaminate structure. The etchant is selected to etch only the first andthird metal foils, and not the middle patterned metal. After etching, afree standing structure (234) is left that can be used as an acousticdevice. Alternative embodiments are readily imagined by injectionmolding vents and acoustic ports into the encapsulant.

These embodiments are meant to be illustrative examples and notexhaustive of the types of useful acoustic devices that can be built bypatterning membranes or movable structures over cavities that are withina laminate or lead frame structure, nor of the methods of manufacturingsaid devices.

While the invention is susceptible to various modifications, andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that the invention is not to be limited to the particular formsor methods disclosed, but to the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the appended claims.

1. A device comprising a laminate structure having a plurality of layersincluding conductive and non-conductive layers, and an acousticallysensitive element positioned in a cavity formed in the layers, the beingin electrical contact with one or more conductive layers of theplurality of layers.
 2. The device of claim 1 with a second laminatecovering the cavity.
 3. The device of claim 1 further comprising one ormore electronic chips bonded to the laminate and electrically connectedto conductive elements on the laminate.
 4. An acoustic elementcomprising a laminate layer having a thin diaphragm layer suspendedabove a conductive base layer.
 5. The acoustic element of claim 4wherein the thin diaphragm is made from a conductive material forming acapacitor.
 6. The acoustic element of claim 4 wherein the thin diaphragmis made from an insulating material that is given an electric charge 7.The acoustic element of claim 4 wherein the thin diaphragm includes oneor more openings.
 8. The acoustic element of claim 4 wherein the thindiaphragm is connected to a second conductive layer in the laminate, thesecond conductive layer being patterned to produce an electrical traceconnectable to other conductive traces in the laminate.
 9. An acousticelement comprising a laminate layer supporting resonating elements. 10.The element of claim 9 wherein the resonating elements are cantilevers.11. The element of claim 9 wherein the resonating elements are suspendedabove a conducting layer in the laminate.
 12. An acoustic elementcomprising a laminate layer supporting a thin conductive ribbonmaterial.
 13. The element of claim 12 wherein the ribbon is shaped toform a corrugated structure.
 14. A microelectronic package a standardlaminate substrate, one or more microelectronic chips mounted on thesubstrate and electrically connected to conductors on the surface of thesubstrate, one or more spacers positioned around the edges of thesubstrate, a top laminate comprising an acoustic element, the spacerproviding a vertical offset between the laminate and the substrate andproviding electrical connections from the bottom substrate to the toplaminate.
 15. A method for building an acoustic element within alaminate structure comprising the steps of forming a first laminatestructure having a first laminate layer with a first metal foil bondedto the laminate layer, patterning a second metal foil over the firstmetal foil, forming a second laminate structure having a second laminatelayer with a cavity formed therein and a third metal foil bonded to thesecond laminate layer beneath the cavity, bonding the first and secondlaminate structures together placing the patterned second metal foilover the cavity, forming an opening in the first laminate layer toexpose the first metal foil, introducing a chemical etchant through theopening to etch away the first metal foil leaving the patterned secondmetal foil, wherein a portion of the patterned second metal foilfreestanding and movable.
 16. The method of claim 15 wherein the secondlaminate structure includes a charged electret material in the secondlaminate layer below the cavity.
 17. The method of claim 15 wherein thecavity in the second laminate structure passes through the secondlaminate layer exposing the third metal foil leaving an air gap betweenportions of the second and third metal foils.
 18. The method of claim 17further comprising the step of patterning a fourth metal foil on thethird metal foil between the third metal foil and the second laminatestructure.
 19. A method for building an acoustic element within alaminate structure comprising the steps of bonding a first metal foil ona surface of a first laminate layer, patterning a second metal foil on atop of the first metal foil, bonding a second laminate layer to thefirst laminate layer, the second laminate layer having an openingexposing the second metal foil, introducing a chemical etchant throughthe opening to etch away the first metal foil leaving the patternedsecond metal foil, wherein a portion of the patterned second metal foilfreestanding and movable.
 20. The method of claim 19 further comprisingthe step of patterning a third metal foil on the bottom of the firstmetal foil between the first metal foil and the first laminate layer.21. The method of claim 19 wherein the second first laminate layerincludes a charged electret material.
 22. A method of packaging amicroacoustic elelment element on a lead frame comprising the steps offorming a lead frames having a body with openings passing through thebody, forming a laminate structure comprising a first metal film with asecond metal film patterned on top of the first metal film and a thirdmetal film bonded to the top of the second metal film, wherein the firstand third metal film comprise a metal that is different from the metalof the second metal film, bonding the laminate structure to the leadframe above the openings in the body, mounting and electricallyconnecting microelectronic components to the lead frame, encapsulatingthe lead frame, laminate structure and microelectronic components in aprotective enclosure, and passing etchant through the holes in the bodyof the lead frame to etch the laminate structure to etch the first andthird metal films leaving a portion of the second metal filmfreestanding and moveable.